my chickens are turning into little piggies!

I let the girls out every morning and they free range until evening everyday. It used to be I'd see them all over the yard scratching up the leaves to look for food but the past couple of days they've eaten the feeder dry them laid around in the sun all day. Not much scratching and foraging activity. And 4 of them won't even leave the coop! They roost and eat then roost and eat again. What's going on? Should I make them leave the coop? I should add that the 4 that won't leave the coop are the only egg layers, the rest are too young. Also they aren't laying eggs. Help!